Method, apparatus and system for transmitting and receiving client signals

ABSTRACT

The present invention provides a method, apparatus and system for transmitting and receiving a client signal. A client signal is mapped to a low-order ODU via a GFP scheme, wherein the low-order ODU is sized to M equal sized timeslots of a high-order OPUk, wherein the high-order OPUk is divided into N equal sized timeslots, wherein M is any one of a group from 1 to N; wherein if k=2, then N=8, if k=3, then N=32 and if k=4, then N=80. The low-order ODU with the client signal is mapped to M equal sized timeslots of the high-order OPUk via a GMP scheme; and an OTU with the high-order OPUk and overheads is formed, and then the OTU is transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/721,338, filed on Mar. 10, 2010, which is a continuation ofInternational Patent Application No. PCT/CN2009/072449, filed on Jun.25, 2009. The International Application claims priority to ChinesePatent Application No. 200810111493.0, filed on Jun. 26, 2008. Theaforementioned patent applications are hereby incorporated by referencein their entireties.

FIELD OF THE INVENTION

The present invention relates to the field of optical network, andparticularly, to a method, apparatus and system for transmitting andreceiving client signals.

BACKGROUND

As the core technology of the next generation transport networks, theOptical Transport Network (OTN) not only has abundant OperationAdministration and Maintenance (OAM), strong Tandem Connection Monitor(TCM) and out-band Forward Error Correction (FEC) capability, but alsocan perform flexible scheduling and management of large volume service,and has increasingly become a major technology of the backbone transportnetworks.

With the rapid development of types of data service, operators hope theOTN to provide better support to data of multiple services, such asclient signals of Ethernet, fiber channel (FC) and Synchronous DigitalHierarchy (SDH), etc.

Conventionally, in the related art, transmission of different types ofclient signals are realized by using Optical Channel Data Unit-k (ODUk),where k=1, 2, 3, 4. At the transmitting end, a client signal to betransmitted is mapped into the ODUk, an overhead is added to the ODUk toform an Optical Channel Transport Unit-k (OTUk) frame, and the OTUkframe is transferred to the OTN for transmission, where k=1, 2, 3, 4.

However, the inventor finds that, the rates of four ODUk (k=1,2,3,4) arepredetermined, with the rate of ODU1 being 2.5G, the rate of ODU2 being10G, the rate of ODU3 being 40G, and the rate of ODU4 being 112G. Inmapping the client signal to be transmitted to the ODUk at thetransmitting end, the rate of the ODUk and the rate of the client signalto be transmitted cannot be matched accurately. Thus the bandwidth ofOTN transport channel is seriously wasted. Meanwhile, for multipleclient signals, the transmitting end has to bundle these multiple clientsignals together and map them into a single ODUk, which is inconvenientfor the OTN to manage each client signal.

SUMMARY OF THE INVENTION

The embodiments of the present invention provides a method, apparatusand system for transmitting and receiving client signals, so that therate of the client signals and the rate of the ODUk can be accuratelymatched, the bandwidth of the OTN transport channel can be saved, and astrong management can be achieved for each client signal.

The embodiments of the present invention provide technical solutions asfollows:

A method for transmitting client signals, including: (1) mapping aclient signal to be transmitted to a corresponding low-order OpticalChannel Data Unit (ODU) in a low-order ODU set, where low-order ODUs inthe low-order ODU set have rates increased in order, and have ratecorrespondence relations with the client signals; (2) mapping thelow-order ODU to a timeslot of a high-order Optical Channel Payload Unit(OPU) in a high-order OPU set; and (3) adding an overhead to thehigh-order OPU to form an Optical Channel Transport Unit (OTU), andtransferring the OTU to an Optical Transport Network (OTN) fortransmission.

An apparatus for transmitting client signals, including: (1) a firstmapping unit, configured to map a client signal to be transmitted to acorresponding low-order Optical Channel Data Unit (ODU) in a low-orderODU set, where low-order ODUs in the low-order ODU set have ratesincreased in order, and have rate correspondence relations with theclient signals; (2) a second mapping unit, configured to map thelow-order ODU obtained by the first mapping unit to a timeslot of ahigh-order Optical Channel Payload Unit (OPU) in a high-order OPU set;and (3) a transmitting unit, configured to add an overhead to thehigh-order OPU obtained by the second mapping unit to form an OpticalChannel Transport Unit (OTU), and transfer the OTU to an OpticalTransport Network (OTN) for transmission.

A method for receiving client signals, including: (1) receiving a dataframe to obtain high-order Optical Channel Payload Units (OPUs) in ahigh-order OPU set; (2) de-mapping the high-order OPUs to obtainlow-order Optical Channel Data Units (ODUs) having rates increased inorder in a low-order ODU set; and (2) de-mapping, according tocorrespondence relations between the client signals and the low-orderODUs in the low-order ODU set, the low-order ODUs in the low-order ODUset to obtain the client signals.

An apparatus for receiving client signals, including: (1) a receivingunit, configured to receive a data frame to obtain high-order OpticalChannel Payload Units (OPUs) in a high-order OPU set; (2) a firstde-mapping unit, configured to de-map the high-order OPUs to obtainlow-order Optical Channel Data Units (ODUs) having rates increased inorder in a low-order ODU set; and (3) a second de-mapping unit,configured to de-map, according to correspondence relations between theclient signals and the low-order ODUs in the low-order ODU set, thelow-order ODUs in the low-order ODU set to obtain the client signals.

A system for communicating client signals, including a transmittingapparatus and a receiving apparatus.

In the embodiments of the present invention, at the transmitting end, alow-order ODU set having rates increased in order is configured,correspondence relations between the client signals to be transmittedand the low-order ODUs in the low-order ODU set are established by rate,and the client signals to be transmitted are mapped into correspondinglow-order ODUs in the low-order ODU set. Thus, the rates of the clientsignals can be accurately matched with the rates of the low-order ODUsin the low-order ODU set, so that the bandwidth of the OTN transportchannel can be saved.

In addition, the transmitting end may, based on the correspondencerelation between the client signals to be transmitted and the low-orderODUs having rates increased in order in the low-order ODU set, mapmultiple client signals to corresponding low-order ODUs in the low-orderODU set, then map each low-order ODUs in the low-order ODU set todifferent timeslots of the high-order OPUs in the high-order OPU set, tobe transferred to the OTN through data frame for transmission, so as tofacilitate the OTN to manage each client signal. Furthermore, the subdata units in the low-order ODU set employ the identical framestructure, so that a strong management can be achieved for each type ofclient signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a client signal transmitting method accordingto a first embodiment of the present invention;

FIG. 2 is a flowchart of a client signal transmitting method accordingto a second embodiment of the present invention;

FIG. 3 is a flowchart of a client signal transmitting method accordingto a third embodiment of the present invention;

FIG. 4 is a structural diagram of a client signal transmitting apparatusaccording to a first embodiment of the present invention;

FIG. 5 is a flowchart of a client signal receiving method according to afirst embodiment of the present invention;

FIG. 6 is a flowchart of a client signal receiving method according to asecond embodiment of the present invention;

FIG. 7 is a flowchart of a client signal receiving method according to athird embodiment of the present invention;

FIG. 8 is a structural diagram of a client signal receiving apparatusaccording to a first embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention are described in detail belowwith reference to the drawings.

Referring to FIG. 1, illustrated is a flowchart of a client signaltransmitting method according to a first embodiment of the presentinvention, which includes:

Step 101: mapping, according to the correspondence relations betweenclient signals to be transmitted and low-order Optical Channel DataUnits (ODUs) having rates increased in order in a low-order ODU set, theclient signals to be transmitted to corresponding low-order ODUs;

Step 102: mapping the low-order ODUs to timeslots of high-order OpticalChannel Payload Units (OPUs) in a high-order OPU set; and

Step 103: adding overheads to the high-order OPUs to form an OpticalChannel Transport Unit (OTU), and transferring the OTU to an OpticalTransport Network (OTN) for transmission.

From the above embodiment, it can be seen that by configuring alow-order ODU set with rates increased in order, and establishingcorrespondence relations between the client signals and the low-orderODUs in the low-order ODU set by rate, a client signal to be transmittedof any rate can be mapped into a corresponding low-order ODU in thelow-order ODU set, besides, the rate of the client signal to betransmitted can be accurately matched with the rate of the low-order ODUin the low-order ODU set, so that the bandwidth of the OTN transportchannel can be saved. Meanwhile, multiple client signals are mapped intodifferent low-order ODUs in the low-order ODU set respectively, then thedifferent low-order ODUs in the low-order ODU set are mapped intodifferent timeslots of the high-order OPUs in the high-order OPU set,and are transferred to the OTN through data frame for transmission. Inthis manner, it is convenient for the OTN to manage each client signal.

Referring to FIG. 2, illustrated is a flowchart of a client signaltransmitting method according to a second embodiment of the presentinvention, which includes:

Step 201: mapping, according to the correspondence relations betweenclient signals to be transmitted and Optical Channel Data Unit-xt(ODUxt) (x=1, 2, . . . N) having rates increased by a natural numbermultiple in an ODUxt set, a client signal to be transmitted to the ODUxtcorresponding to the rate of the client signal; where, an ODUxt (x=1, 2,. . . N) set having rates increased in order is configured. With respectto a specific client signal, an ODUxt corresponding to the rate of theclient signal is selected from the ODUxt (x=1, 2, . . . N) set accordingto the rate of the client signal, and then the client signal is mappedinto the ODUxt.

Preferably, in the ODUxt (x=1, 2, . . . N) set, the rate of a minimumrate granularity ODU1t is the rate of a minimum timeslot granularity ina High Order Optical Channel Data Unit-k (HO ODUk) (k=1, 2, 3, 4) set,and the embodiments of the present invention do not intend to limit thespecific rate of the minimum rate granularity ODU1t in the ODUxt set.Currently, the International Telecommunication Union (ITU) is indiscussion about setting a new OTN rate, for HO OPU1, a possible optionis setting the rate as 238/227×2.488320 Gbit/s, i.e. about 2.6088993833Gbit/s. For the new OTN rate, if HO ODU1 is divided into 2 timeslots,the rate of the minimum timeslot granularity in the HO ODUk (k=1, 2, 3,4) set is half of that of the HO OPU1, i.e. 1.304449692 Gbit/s. Thus therate of ODU1t is the rate of the minimum timeslot granularity in the HOODUk (k=1, 2, 3, 4) set, i.e. 1.304449692 Gbit/s. The rate of ODUxt is anatural number multiple of the rate of ODU1t, i.e. x xODU1t (x=1, 2, . .. N).

Another possible option is setting the rate of the minimum rategranularity ODU1t in the ODUxt set to be the same as that of ODU0 beingcurrently discussed by the ITU, then ODUxt set will be a set of rateswhich are increased in order by a multiple of the rate of ODU0.Presently, there are two possible options for the rate of ODU0: about1.249 Gbit/s or about 1.244 Gbit/s. The adoption of such rate has anadvantage of being compatible with the existing ODUk, so that ODU1t canbe introduced to all the OTN containers.

The embodiments of the present invention do not intend to limit theframe structure of ODUxt, and preferably, it is suggested that the framestructure defined by G.709 be adopted as the ODUxt frame structure, andthat the frequency offset of ODUxt signal also be matched with thecurrent G.709, i.e., +/−20 ppm.

When the rate of ODU1t is 1.304449692 Gbit/s, the correspondencerelations between the current client signals and ODUxt are as shown inTable 1.

TABLE 1 Correspondence Relations between the Current Client signals andODUxt Rate of Client signal Type of Rate of ODUxt Type of Client signal(Gbit/s) ODUxt (Gbit/s) Fiber Channel 0.53125 ODU1t 1.304449692 FC-1G1.065 ODU1t 1.304449692 GE 1.25 ODU1t 1.304449692 HDTV 1.485 ODU2t2.608899383 FC-2G 2.125 ODU2t 2.608899383 STM-16 2.488320 ODU2t2.608899383 ODU1 2.498775 ODU2t 2.608899383 FC-4G 4.25 ODU4t 5.217798767FC-8G 8.5 ODU7t 9.131147841 STM-64 9.95328 ODU8t 10.43559753 ODU210.037273924 ODU8t 10.43559753 10GE LAN 10.3125 ODU8t 10.43559753 FC-10G10.52 ODU9t 11.74004722 100GE-5L 20.625 ODU16t 20.87119507 100GE-4L25.78125 ODU20t 26.08899383 STM-256 39.81312 ODU31t 40.43794044 ODU340.319218983 ODU31t 40.43794044 40GE 41.25 ODU32t 41.74239013 100GE103.125 ODU80t 104.3559753

In order to ensure a full rate transparent transport of the clientsignal, and in consideration of the requirement for timing transparenttransport of synchronous Ethernet, multiple client signals can beregarded as Constant Bit Rate (CBR) client signals. In step 201, eachtype of CBR client signal can be mapped into corresponding ODUxt,through asynchronous mapping such as Generic Mapping Procedure (GMP) orNJO/PJO asynchronous adjustment. For a packet type client signal, it maybe packaged with a Generic Framing Procedure (GFP), and the packagedpacket type client signal may be mapped into corresponding ODUxtaccording to a selected ODUxt bandwidth, by inserting IDEL frames.

Step 202: mapping the ODUxt bearing the client signals to timeslots ofcorresponding HO ODUk in the HO ODUk (k=1, 2, 3, 4) set; where, if therate of the minimum timeslot granularity in the HO ODUk (k=1, 2, 3, 4)set is 1.304449692 Gbit/s, the number of timeslots obtained by dividingthe HO ODUk in the HO ODUk (k=1, 2, 3, 4) set and their correspondencewith the types of ODUxt are shown in the following Table 2.

TABLE 2 Number of Timeslots in HO ODUk and Correspondence with ODUxtType of Number of HO ODUk Rate Level Timeslots Type of born ODUxt HOODU1 2.5 G 2 ODU1t, ODU2t HO ODU2 10 G 8 ODU1t, ODU2t . . . ODU8t HOODU3 40 G 32 ODU1t, ODU2t . . . ODU32t HO ODU4 112 G 80 ODU1t, ODU2t . .. ODU80t

According to Table 2 and taking HO ODU1 as an example, HO ODU1 isdivided into 2 timeslots, where one HO ODU1 can bear two ODU1ts or oneODU2t. When one HO ODU1 bears two ODU1ts, each HO ODU1 timeslot bearsone ODU1t, and when one HO ODU1 bears one ODUt, the two HO ODU1timeslots are bound together to form a timeslot group to bear one ODUtjointly.

In step 202, the ODUxt can be mapped into a timeslot or timeslot groupof the HO ODUk through synchronous mapping or asynchronous mapping,where the asynchronous mapping can be carried out in a way of NJO/PJOasynchronous adjustment, or in a way of GMP.

Step 203: adding overheads to the HO ODUk bearing the client signals toform HO OTUk.

Step 204: transferring the HO OTUk to the OTN for transmission.

From the above embodiment, it can be seen that an ODUxt (x=1, 2, . . .N) set having rates increased in order is configured at the transmittingend, and correspondence relations between the client signals and theODUxt in the ODUxt (x=1, 2, . . . N) set are established by rate, thus aclient signal of any rate to be transmitted can be mapped into acorresponding ODUxt in the ODUxt (x=1, 2, . . . N) set, besides, therate of the client signal to be transmitted can be accurately matchedwith the rate of the ODUxt in the ODUxt (x=1, 2, . . . N) set, so thatthe bandwidth of the OTN transport channel can be saved. Meanwhile,since the rates of respective ODUxt in the ODUxt (x=1, 2, . . . N) setare increased in order to show a regularity, the mapping of each ODUxtto the HO ODUk does not need a complicated adjustment and can beperformed simply. The configured ODUxt (x=1, 2, . . . N) set can beflexibly adapted to each type of client signal, and provide a completelytransparent mapping for the client signal. Further, the transmitting endmaps multiple client signals to different ODUxts in the ODUxt (x=1, 2, .. . N) set respectively, and transmits the ODUxts after mapping them todifferent timeslots of the HO ODUk in the HO ODUk (k=1, 2, 3, 4) set, sothat it is convenient for the OTN to manage each client signal. Inaddition, the ODUxts in the ODUxt (k=1, 2, 3, 4) set employ theidentical frame structure, so that a strong management can be achievedfor each type of client signal.

A flowchart for a client signal transmitting method according to a thirdembodiment of the present invention is described in detail withreference to FIG. 3. In the present embodiment, the rate of ODU1t is1.304449692 Gbit/s, HO ODU1 is divided into 2 timeslots, HO ODU2 isdivided into 8 timeslots, HO ODU3 is divided into 32 timeslots, and HOODU4 is divided into 80 timeslots. Four client signals are to betransmitted, including 2 10GE LAN, 1 STM-64, and 1 ODU2. The methodincludes:

Step 301: mapping, according to the correspondence relations betweenclient signals to be transmitted and ODUxts having rates increased by anatural number multiple in the ODUxt (x=1, 2, . . . N) set, the 4 clientsignals to 4 ODU8ts respectively, through GMP asynchronous mapping.

In the present embodiment, the rate of ODU1t is 1.304449692 Gbit/s,therefore 4 client signals are mapped into an ODU8t according to thecorrespondence relations in Table 1 between the current client signalsand the ODUxts in the ODUxt(x=1, 2, . . . N) set, so as to

Here, 1 10GE LAN client signal is packed in ODU8t-a, 1 10GE LAN clientsignal is packed in ODU8t-b, 1 STM-64 client signal is packed inODU8t-c, and 1 ODU2 client signal

The frequency differences between the client signals and the ODU8t canbe absorbed by using a GMP mapping method. The mapping method is tocalculate a byte number Cn of client signals born by the ODU8t in oneframe period, based on the clock relation between the client signals andthe ODU8t, then map Cn value to an overhead area of the ODU8t, and mapsCn bytes to the ODU8t by Sigma-Delta algorithm.

Step 302: mapping 4 ODU8ts to 4 timeslot groups formed by bonding every8 timeslots in HO ODU3, respectively, through NJO/PJO asynchronousmapping.

In step 302, each ODU8t is mapped into a timeslot group formed bybonding 8 timeslots, and therefore the 4 ODU8ts are all mapped into 32timeslots in HO ODU3.

Step 303: adding an overhead to HO ODU3 bearing the 4 client signals toform HO OTU3.

Step 304: transferring HO OTU3 to the OTN for transmission.

Corresponding to the above described method, an embodiment of thepresent invention further provides a client signal transmittingapparatus. Referring to FIG. 4, illustrated is a structural diagram of aclient signal transmitting apparatus according to a first embodiment ofthe present invention. The transmitting apparatus in the presentembodiment includes a first mapping unit 401, a second mapping unit 402and a transmitting unit 403. The internal structure and connectionrelations of the transmitting apparatus are further described below inconjunction with its operating principle.

The first mapping unit 401 is configured to map, according to thecorrespondence relations between client signals to be transmitted andlow-order ODUs having rates increased in order in a low-order ODU set,the client signals to be transmitted to corresponding low-order ODUs.

The second mapping unit 402 is configured to map the low-order ODUsobtained by the first mapping unit 401 to timeslots of high-order OPUsin a high-order OPU set; and

The transmitting unit 403 is configured to add overheads to thehigh-order OPUs obtained by the second mapping unit 402 to form an OTU,and transfer the OTU to OTN for transmission.

From the above embodiment, it can be seen that the first mapping unitmaps, according to the correspondence relations between the clientsignals to be transmitted and low-order ODUs having rates increased inorder in the low-order ODU set, a client signal of any rate to betransmitted to a corresponding low-order ODU in the low-order ODU set,thus, the rates of the client signals to be transmitted can beaccurately matched with the rates of the low-order ODUs in the low-orderODU set, so that the bandwidth of the OTN transport channel can besaved. Meanwhile, since the rates of the low-order ODUs in the low-orderODU set are increased in order to show a regularity, the mapping of thelow-order ODUs in the low-order ODU set to the timeslots of thehigh-order OPU in the high-order OPU set by the second mapping unit donot need complicated adjustments and can be performed simply. Theconfigured low-order ODU set can be flexibly adapted to each type ofclient signal, and provide a completely transparent mapping for theclient signal. Further, the first mapping unit maps client signals to betransmitted to corresponding low-order ODUs in the low-order ODU set,respectively, then maps the low-order ODUs in the low-order ODU set todifferent timeslots of the high-order OPUs in the high-order OPU set, tobe transferred to the optical transport network OTN through data framefor transmission, so that it is convenient for the OTN to manage eachclient signal. In addition, the low-order ODUs in the low-order ODU setuse the identical frame structure, so that a strong management can beachieved for each type of client signal.

Referring to FIG. 5, illustrated is a flowchart of a client signalreceiving method according to a first embodiment of the presentinvention, which includes:

Step 501: receiving data frames to obtain high-order OPUs in ahigh-order OPU set;

Step 502: de-mapping the high-order OPUs to obtain low-order ODUs havingrates increased in order in a low-order ODU set; and

Step 503: de-mapping, according to correspondence relations betweenclient signals and the low-order ODUs in the low-order ODU set, thelow-order ODUs in the low-order ODU set to obtain the client signals.

From the above embodiment, it can be seen that at the receiving end,similarly, a low-order ODU set having rates increased in order isconfigured, the low-order ODUs in the low-order ODU set are de-mappedaccording to the correspondence relations between the rates of theclient signals to be transmitted and the low-order ODUs in the low-orderODU set, to obtain corresponding client signals born on the low-orderODUs in the low-order ODU set. Accordingly, the rates of the clientsignals can be accurately matched with the rates of the low-order ODUsin the low-order ODU set, so that the bandwidth of the OTN transportchannel can be saved. Meanwhile, since the rates of the low-order ODUsin the low-order ODU set are increased in order to show a regularity,the de-mapping from the high-order OPUs in the high-order OPU set to thelow-order ODUs in the low-order ODU set do not need complicatedadjustments, and can be performed simply.

Referring to FIG. 6, illustrated is a flowchart of a client signalreceiving method according to a second embodiment of the presentinvention, which includes:

Step 601: receiving HO OTUk through a network interface;

Step 602: parsing overheads of the HO OTUk to obtain HO ODUk bearingclient signals;

Step 603: de-mapping the HO ODUk to obtain ODUxt; and

Step 604: de-mapping the ODUxt to obtain the client signals, accordingto the correspondence relations between the client signals and the ODUxthaving rates increased by a natural number multiple in an ODUxt (x=1, 2,. . . N) set.

From the above embodiment, it can be seen that at the receiving end,similarly, an ODUxt (x=1, 2, . . . N) set with rates increased by anatural number multiple is configured. Corresponding client signals bornin the ODUxt can be obtained by de-mapping the ODUxt according to thecorrespondence relations between the rates of the client signals to betransmitted and the ODUxt in the ODUxt (x=1, 2, . . . N) set. Thus, therates of the client signals can be accurately matched with the rates ofthe ODUxt in the ODUxt (x=1, 2, . . . N) set, so that the bandwidth ofthe OTN transport channel can be saved. Meanwhile, since the rates ofthe ODUxt in the ODUxt (x=1, 2, . . . N) set are increased in order toshow a regularity, the de-mapping from the HO ODUk to the ODUxt do notneed complicated adjustments, and can be achieved simply.

A flowchart of a client signal receiving method according to a thirdembodiment of the present invention is described in detail withreference to FIG. 7. The receiving method includes:

Step 701: receiving HO OTU3 through a network interface;

Step 702: parsing an overhead of the HO OTU3 to obtain HO ODU3;

Here the HO ODU3 is divided into 32 timeslots which in turn form 4timeslot groups, each timeslot group being formed by bonding 8timeslots. The 4 timeslot groups respectively bear ODU8t-a, ODU8t-b,ODU8t-c and ODU8t-d which are packed with client signals. Here, ODU8t-ais packed with 1 10GE LAN client signal, ODU8t-b is packed with 1 10GELAN client signal, ODU8t-c is packed with 1 STM-64 client signal, andODU8t-d is packed with 1 ODU2 client signal.

Step 703: de-mapping the HO ODU3 through NJO/PJO asynchronous de-mappingto obtain 4 ODU8ts;

Step 704: de-mapping the 4 ODU8ts respectively through GMP asynchronousde-mapping to obtain 4 client signals, according to the correspondencerelations between the client signals and the ODUxt having ratesincreased by a natural number multiple in the ODUxt (x=1, 2, . . . N)set.

Corresponding to the above described method, the embodiments of thepresent invention further provide a client signal receiving apparatus.Referring to FIG. 8, illustrated is a structural diagram of a clientsignal receiving apparatus according to a first embodiment of thepresent invention. The receiving apparatus in the present embodimentincludes a receiving unit 801, a first de-mapping unit 802 and a secondde-mapping unit 803. The internal structure and connection relations ofthe receiving apparatus are further described in conjunction with itsoperating principle.

The receiving unit 801 is configured to receive data frames to obtainhigh-order OPUs in a high-order OPU set.

The first de-mapping unit 802 is configured to de-map the high-orderOPUs to obtain low-order ODUs having rates increased in order in alow-order ODU set.

The second de-mapping unit 802 is configured to de-map, according to thecorrespondence relations between client signals and the low-order ODUsin the low-order ODU set, the low-order ODUs in the low-order ODU set toobtain the client signals.

In the first embodiment for communication method of the presentinvention, a client signal communication method is implemented,including the above-mentioned transmitting method and receiving methods,and herein is not described since details are given previously.

Corresponding to the above described method, the present inventionfurther provides a first embodiment of a client signal transmissionsystem, including the previous receiving apparatus and transmittingapparatus, and herein is not described since details are givenpreviously.

The structural elements illustrated in FIGS. 4 and 8 are implemented onone or more general purpose computers or digital processors usingstandard or proprietary computer operating systems and program codes.For example, the structural elements can be implemented by ASIC, FPGA orprogrammable chip.

The above described contents are just some exemplary embodiments of thepresent invention. It should be noted that, a person skilled in the artcan make various changes and modifications without deviating from theprinciple of the present invention, and these changes and modificationsshall also be regarded as falling within scope of the present invention.

What is claimed is:
 1. A method for transmitting client signals, themethod comprising: mapping a client signal to a low-order OpticalChannel Data Unit (ODU) via a Generic Framing Procedure (GFP) scheme,wherein the low-order ODU is sized to M equal sized timeslots of ahigh-order Optical Channel Payload Unit-k (OPUk), wherein the high-orderOPUk is divided into N equal sized timeslots, wherein M is any one of anumber group from 1 to N; wherein if k=2, then N=8, if k=3, then N=32,and if k=4, then N=80; mapping the low-order ODU with the client signalto M equal sized timeslots of the high-order OPUk via a Generic MappingProcedure (GMP) scheme; forming an Optical Channel Transport Unit (OTU)with the high-order OPUk and overheads; and transmitting the OTU.
 2. Themethod according to claim 1, wherein the size of the low-order ODU islarger than the size of an Optical Channel Data Unit-k-1 (ODUk-1) andless than the size of an Optical Channel Data Unit-k (ODUk).
 3. Themethod according to claim 2, wherein a bit rate of the client signal islarger than a bit rate of the ODUk-1 and less than a bit rate of theODUk.
 4. The method according to claim 1, further comprising: mapping asecond client signal to a second low-order ODU, wherein the secondlow-order ODU has a size of L equal sized timeslots of the high-orderOPUk, wherein the L+M is equal or less than N; and mapping the secondlow-order ODU to L equal sized timeslots of the high-order OPUk.
 5. Anapparatus comprising a transmitter configured to couple to a receiverand to transmit client signals to the receiver, wherein the transmitteris configured to: map a client signal to a low-order Optical ChannelData Unit (ODU) via a Generic Framing Procedure (GFP) scheme, whereinthe low-order ODU is sized to M equal sized timeslots of a high-orderOptical Channel Payload Unit-k (OPUk), wherein the high-order OPUk isdivided into N equal sized timeslots, wherein M is any one of a numbergroup from 1 to N; wherein if k=2, then N=8, if k=3, then N=32, and ifk=4, then N=80; map the low-order ODU with the client signal to M equalsized timeslots of the high-order OPUk via a Generic Mapping Procedure(GMP) scheme; form an Optical Channel Transport Unit (OTU) with thehigh-order OPUk and overheads; and transmit the OTU.
 6. The apparatusaccording to claim 5, wherein the size of the low-order ODU is largerthan the size of an Optical Channel Data Unit-k-1 (ODUk-1) and less thanthe size of an Optical Channel Data Unit-k (ODUk).
 7. The apparatusaccording to claim 6, wherein a bit rate of the client signal is largerthan a bit rate of the ODUk-1 and less than a bit rate of the ODUk. 8.The apparatus according to claim 5, wherein the transmitter isconfigured to: map a second client signal to a second low-order ODU,wherein the second low-order ODU has a size of L equal sized timeslotsof the high-order OPUk, wherein the L+M is equal or less than N; and mapthe second low-order ODU to L equal sized timeslots of the high-orderOPUk.
 9. A system, comprising: a transmitter is configured to: map aclient signal to a low-order Optical Channel Data Unit (ODU) via aGeneric Framing Procedure (GFP) scheme, wherein the low-order ODU issized to M equal sized timeslots of a high-order Optical Channel PayloadUnit-k (OPUk), wherein the high-order OPUk is divided into N equal sizedtimeslots, wherein M is any one of a number group from 1 to N; whereinif k=2, then N=8, if k=3, then N=32, and if k=4, then N=80, map thelow-order ODU with the client signal to M equal sized timeslots of thehigh-order OPUk via a Generic Mapping Procedure (GMP) scheme, form anOptical Channel Transport Unit (OTU) with the high-order OPUk andoverheads, and transmit the OTU; and a receiver is configured to:receive the OTU, de-map the OTU to get the low-order ODU, and de-map thelow-order ODU to get the client signal.
 10. The system according toclaim 9, wherein the size of the low-order ODU is larger than the sizeof an Optical Channel Data Unit-k-1 (ODUk-1) and less than the size ofan Optical Channel Data Unit-k (ODUk).
 11. The apparatus according toclaim 10, wherein a bit rate of the client signal is larger than a bitrate of the ODUk-1 and less than a bit rate of the ODUk.
 12. Theapparatus according to claim 9, wherein the transmitter is furtherconfigured to: map a second client signal to a second low-order ODU,wherein the second low-order ODU has a size of L equal sized timeslotsof the high-order OPUk, wherein the L+M is equal or less than N; and mapthe second low-order ODU to L equal sized timeslots of the high-orderOPUk.